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Cummingtonite (Photo) [abbr. Cum ]

Year of discovery: 1824 (Cummington, USA), 1937 (Japan)

Locality list: 182 localities of cummingtonite

• Mg₇Si₈O₂₂(OH)₂
• [][Mg²⁺₂][Mg²⁺₃][Mg²⁺₂][(OH)₂|(Si₄O₁₁)₂]^14-

• Class: Mg-Fe-Mn amphibole subgroup < w(OH,F,Cl)-dominant amphibole group < Amphibole supergroup
• Class: Inosilicate (Double chain) - Hydroxide
• One of minerals called Asbestos.

• Polymorph: Anthophyllite (Orthorhombic), Proto-anthophyllite (Orthorhombic)

• Mg₂ => Mn₂: Mangano-cummingtonite
• Mg₂ => Ca₂: Tremolite, Actinolite

• Mg => Fe: Ferro-anthophyllite (Series), Grunerite, Proto-ferro-anthophyllite

• MgSi => AlAl: Gedrite (Series)

• Color: Dark green, Brown
• Streak: Grayish white
• Luster: Vitreous
• Diaphaneity: Translucent

• Habit: Acicular, Prismatic

• Cleavage: Perfect on {110} (2 planes, 120 degree)
• Hardness: 5-6
• Density: 3.2

• System: Monoclinic
• Group: 2/m, C2/m
• Lattice: a=9.5, b=18.2, c=5.3, β=102.0

Synonym: Amosite